Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps. In many submersible pumping systems, rotating shafts are used to transfer power from the prime mover to output devices like gas separators and pump assemblies. Each of the components and sub-components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment, which includes wide ranges of temperature, pressure and corrosive well fluids.
Submersible pumping systems can also include seal sections connected between the motor and the pump assembly. The seal section protects the motor from well fluids and thrust forces generated by the operation of the motor and pump. During operation, the motor produces heat that is in part dissipated into circulating lubricant. Thermal expansion causes the volume of the lubricant to increase at elevated temperatures. To prevent the accumulation of pressure within the motor, lubricant is vented into the adjacent lubricant filled seal section. As the motor cools, the motor lubricants contract and well fluids are drawn into the seal section to replace the volume of motor lubricant that returned to the motor. As fluids exchange place in the seal section, the motor oil may become contaminated by mixing with the well bore fluid.
Mechanical seals are commonly used to prevent the migration of well bore fluid along the rotating shafts. Generally, a mechanical seal includes components that provide a structural barrier against fluid migration. A popular design of mechanical seals employs a spring on the exterior of the mechanical seal that exerts axial force on components of the mechanical seal. The spring keeps the components of the mechanical seal in proper position to keep the well bore fluids from migrating along the shaft.
Turning to FIG. 1, shown therein is a PRIOR ART seal section 212 of the type disclosed in U.S. Pat. No. 7,344,356, entitled “Mechanical Seal With Bellows Seating Alignment,” issued Mar. 18, 2008 and commonly assigned with the present application. The PRIOR ART seal section 212 includes a head 214 configured for attachment to a pump assembly (not shown), a base 216 configured for attachment to a motor assembly (not shown), a rotating shaft 226 and a plurality of mechanical seals 224a, 224b, 224c and 224d disposed within the seal section 212 at various points along the rotating shaft 226. The head 214 includes a mechanical seal chamber 238 that houses the uppermost mechanical seal 224a. 
While generally acceptable, the PRIOR ART design depicted in FIG. 1 may be susceptible to failure in certain environments. As wellbore fluids are drawn into the seal section 212, sand and other particulate solids may collect in the mechanical seal chamber 238 in the proximity of the mechanical seal 224a. Contamination with solid particles degrades the performance characteristics of the mechanical seal spring and compromises the sealing surfaces of the mechanical seal, resulting in a failure of the mechanical seal.
Accordingly, there exists a need for an improved design that is more resistant to contamination and wear caused by solid particles. It is to this and other deficiencies in the prior art that the present invention is directed.